Method of forming a cured elastomer and golf balls

ABSTRACT

A cured elastomer golf ball component is made by heating an elastomer compound containing an ethylenically unsaturated elastomer, an ethylenically unsaturated monomer, and first and second free radical initiators to a first crosslinking temperature T 1  in a compression mold and partially crosslinking the elastomer, then heating to a second crosslinking temperature T 2  and curing the elastomer component of the golf ball. Either: (i) the first initiator has a half-life of about 0.2-5 minutes at T 1 , the second initiator has a half-life of about 0.2-5 minutes at T 2 , and T 2  is higher T 1  by at least about 30° C.; or (ii) the second initiator&#39;s one-minute half-life temperature is at least about 30° C. higher than the first initiator&#39;s one-minute half-life temperature, T 1  is within about 20° C. of the first initiator&#39;s one-minute half-life temperature, and T 2  is within about 20° C. of the second initiator&#39;s one-minute half-life temperature.

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/029,109, filed Sep. 17, 2013, which claims the benefit of ofU.S. Provisional Application No. 61/843,326, filed Jul. 6, 2013; theentire contents of both of these patent applications are herebyincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to methods of forming a cured elastomerand to articles formed from the cured elastomer.

BACKGROUND

This section provides information helpful in understanding the inventionbut that is not necessarily prior art.

Articles formed from cured elastomers may have excellent physicalproperties, such as stability, durability, flexibility, elasticity, andresilience. For example, a core of a golf ball may be formed from acured elastomer and may be configured to provide the golf ball withspecific characteristics, such as compression, spin, velocity, andresilience. As such, golf balls including cores formed from curedelastomers may be optimized for various playing abilities andconditions.

SUMMARY

This section provides a general summary of the disclosure and may not becomprehensive of its full scope or all of the disclosed features.

A method of forming a cured elastomer includes partially crosslinking anelastomer compound at a first crosslinking temperature to form aprecursor compound. The elastomer compound comprises an elastomer, suchas an ethylenically unsaturated elastomer or other thermoplasticelastomer; a first free radical initiator having a first half-life offrom about 0.2 minutes to about 5 minutes at a first crosslinkingtemperature; and a second free radical initiator. The precursor compoundis further crosslinked at a second crosslinking temperature that ishigher than the first crosslinking temperature by at least about 30° C.to thereby form the cured elastomer. The second free radical initiatorhas a second half-life of from about 0.2 minutes to about 5 minutes atthe second crosslinking temperature.

An article comprises a cured elastomer. The cured elastomer is formedfrom a precursor compound and has a final crosslinking density. Theprecursor compound is thermoplastic and is formed from an elastomercompound. The elastomer compound comprises an ethylenically unsaturatedelastomer, a first free radical initiator, and a second free radicalinitiator. The first free radical initiator has a first half-life offrom about 0.2 minutes to about 5 minutes at a first crosslinkingtemperature. The second free radical initiator has a second half-life offrom about 0.2 minutes to about 5 minutes at a second crosslinkingtemperature that is higher than the first crosslinking temperature by atleast about 30° C. The elastomer compound is partially crosslinked atthe first crosslinking temperature to a first crosslinking density thatis at most about 40% of the final crosslinking density. The precursorcompound is further crosslinked at the second crosslinking temperatureto form the cured elastomer.

A method of forming a golf ball includes partially crosslinking anelastomer compound at a first crosslinking temperature to form aprecursor compound. The elastomer compound comprises an ethylenicallyunsaturated elastomer, a first free radical initiator having a firstone-minute half-life temperature, and a second free radical initiatorhaving a second one-minute half-life temperature that is higher than thefirst one-minute half-life temperature by at least about 30° C. Thefirst crosslinking temperature is equal to from about 20° C. lower thanthe first one-minute half-life temperature to about 20° C. higher thanthe first one-minute half-life temperature. The method also includesforming a core by further crosslinking the precursor compound at asecond crosslinking temperature to thereby form a cured elastomer. Thesecond crosslinking temperature is higher than the first crosslinkingtemperature and is equal to from about 20° C. lower than the secondone-minute half-life temperature to about 20° C. higher than the secondone-minute half-life temperature. The method further includes disposinga cover on the core such that the cover surrounds the core to therebyform the golf ball.

A golf ball includes a core comprising a cured elastomer and a coverdisposed on and surrounding the core. The cured elastomer is formed froman elastomer compound comprising an ethylenically unsaturated elastomer,a first free radical initiator having a first one-minute half-lifetemperature, and a second free radical initiator having a secondone-minute half-life temperature that is higher than the firstone-minute half-life temperature by at least about 30° C. The elastomercompound is partially crosslinked at a first crosslinking temperature toform a precursor compound. The first crosslinking temperature is equalto from about 20° C. lower than the first one-minute half-lifetemperature to about 20° C. higher than the first one-minute half-lifetemperature. The precursor compound is further crosslinked at a secondcrosslinking temperature to thereby form the cured elastomer. The secondcrosslinking temperature is higher than the first crosslinkingtemperature and is equal to from about 20° C. lower than the secondone-minute half-life temperature to about 20° C. higher than the secondone-minute half-life temperature.

An elastomer compound for forming a cured elastomer comprises anethylenically unsaturated elastomer, a first free radical initiatorhaving a first one-minute half-life temperature of at least about 120°C. and at most about 170° C., and a second free radical initiator havinga second one-minute half-life temperature that is higher than the firstone-minute half-life temperature by at least about 30° C. The first freeradical initiator is present in the elastomer compound in an amount ofat most about 40 parts by weight based on 100 parts by weight of a totalamount of the first free radical initiator and the second free radicalinitiator.

The cured elastomer, and articles formed from the cured elastomer, mayhave excellent physical properties. For example, the cured elastomer andarticles may have excellent resilience. In particular, partiallycrosslinking the elastomer compound at the first crosslinkingtemperature with the first free radical initiator and furthercrosslinking the precursor compound at the second crosslinkingtemperature with the second free radical initiator may provide the curedelastomer with excellent resilience and softness as compared to othercured elastomers which are not formed by the dual-stage cure anddual-cure temperature methods. For example, golf balls formed by themethods may have excellent coefficients of restitution and elasticity,and may exhibit excellent durability over an operating life andexcellent spin during flight.

The above features and advantages and other features and advantages ofthe present disclosure are readily apparent from the following detaileddescription of the best modes for carrying out the concepts of thedisclosure when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a method of forming a cured elastomer.

FIG. 2 is a schematic illustration of a side view of an articleincluding the cured elastomer formed by the method of FIG. 1.

FIG. 3 is a flowchart of a method of forming a golf ball.

FIG. 4 is a schematic, enlarged, partial cross-sectional view of thegolf ball formed by the method of FIG. 3.

FIG. 5A is a schematic cross-sectional view of a pair of injectionmolding dies for forming a core of a golf ball.

FIG. 5B is a schematic cross-sectional view of a pair of injectionmolding dies having a thermoplastic core of a golf ball formed therein.

FIG. 6A is a schematic cross-sectional view of piece of rubber stock.

FIG. 6B is a schematic cross-sectional view of an intermediate layercold-formed blank.

FIG. 6C is a schematic cross-sectional view of a pair of compressionmolding dies being used to form a pair of cold-formed blanks about ametallic spherical core.

FIG. 6D is a schematic cross-sectional view of a pair of compressionmolding dies being used to compression mold an intermediate layer of agolf ball about a polymeric core.

DETAILED DESCRIPTION

Referring to the Figures, wherein like reference numerals refer to likeor identical elements, a method 10 of forming a cured elastomer is showngenerally in FIG. 1. The method 10 and cured elastomer may be useful forforming any number of elastomer articles 12 (FIG. 2) or components ofelastomer articles 12, such as, but not limited to, golf balls 112 (FIG.4), sporting equipment, footwear components, e.g., outsoles 212 (FIG. 2)and traction elements 312 (FIG. 2) of outsoles 212, vehicle components,construction articles, sound-deadening articles, vibration-dampeningarticles, energy storage devices, resilient foams, furniture components,garden tools, conveyor belts, escalator belts and hand rails, andflooring. More specifically, the cured elastomer is a cured product,e.g., a thermoset, but is formed from a precursor compound that is aprocessable thermoplastic.

In one non-limiting example, the method 10 may be useful for forming acore or a core component, e.g., a center 16 (FIG. 4) or one or moreintermediate layers 18, 19 (FIG. 4), of a golf ball 112. FIG. 4schematically illustrates an exploded, partial cross-sectional view of agolf ball 112. As shown, the golf ball 112 may have a multi-layerconstruction that includes a core with a center 12 surrounded by one ormore intermediate layers 18, 19, and a cover 24 (i.e., where the cover24 surrounds the core and forms an outermost layer of golf ball 112).While FIG. 4 generally illustrates a ball 112 with a four-piececonstruction, the presently described structure and techniques may beequally applicable to three-piece balls, as well as balls with five ormore pieces. In general, the cover 24 may define an outermost layer ofthe ball 112 and may include any desired number of dimples 26,including, for example, between 280 and 432 total dimples, and in someexamples, between 300 and 392 total dimples, and typically between 298to 360 total dimples. As known in the art, the inclusion of dimplesgenerally decreases the aerodynamic drag of the ball, which may providefor greater flight distances when the ball is properly struck.

In a completely assembled ball 112, each layer (including the center 16,cover 24, and one or more intermediate layers 18, 19) may besubstantially concentric with every other layer such that every layershares a common geometric center. Additionally, the mass distribution ofeach layer may be uniform such that the center of mass for each layer,and the ball as a whole, is coincident with the geometric center. In onenon-limiting example, the method 10 may be useful for forming a core ora core component, e.g., a center 16 (FIG. 4) or one or more intermediatelayers 18, 19 (FIG. 4), of a golf ball 112.

As used herein, the terms “a,” “an,” “the,” “at least one,” and “one ormore” are interchangeable and indicate that at least one of an item ispresent. A plurality of such items may be present unless the contextclearly indicates otherwise. All numerical values of parameters (e.g.,of quantities or conditions) in this disclosure, including the appendedclaims, are to be understood as being modified in all instances by theterm “about” whether or not “about” actually appears before thenumerical value. “About” indicates that the stated numerical valueallows some slight imprecision (e.g., with some approach to exactness inthe value; approximately or reasonably close to the value; nearly). Ifthe imprecision provided by “about” is not otherwise understood withthis meaning, then “about” as used herein indicates at least variationsthat may arise from methods of measuring and using such parameters. Inaddition, disclosure of ranges includes disclosure of all values andfurther divided ranges within the entire range. Each value within arange and the endpoints of a range are all disclosed as separateembodiments. In this disclosure, for convenience, “polymer” and “resin”are used interchangeably to encompass resins, oligomers, and polymers.The terms “comprises,” “comprising,” “including,” and “having” areinclusive and therefore specify the presence of stated items, but do notpreclude the presence of other items. As used in this disclosure, theterm “or” includes any and all combinations of one or more of the listeditems. When the terms “first,” “second,” “third,” etc. are used todifferentiate various items from each other, these designations aremerely for convenience and do not limit the items. Further, as usedherein, the terminology “at least” is equivalent to “greater than orequal to,” and the terminology “at most” is equivalent to “less than orequal to.”

Referring again to FIG. 1, the method 10 includes partially crosslinking20 an elastomer compound at a first crosslinking temperature to form theprecursor compound, and further crosslinking 22 the precursor compoundat a second crosslinking temperature that is higher than the firstcrosslinking temperature to thereby form the cured elastomer. That is,the method 10 includes first partially crosslinking 20 the elastomercompound in a first-stage curing operation before subsequently heatingor curing the precursor compound at the higher, second crosslinkingtemperature in a second-stage curing operation.

Elastomer Compound

The method 10 (FIG. 1) may also include compounding or combiningindividual components to form the elastomer compound. For example,individual components may be mixed together in a continuous mixer or abatch mixer, e.g., an intermeshing rotor mixer, such as an Intermixmixer, a twin screw extruder, a tangential rotor mixer such as a Banburymixer, or a two roll mill. The mixer may blend the components togethervia a single step or multiple steps, and may mix the components viadispersive mixing or distributive mixing to form the resulting elastomercompound.

A. Ethylenically Unsaturated Elastomer

More specifically, the elastomer compound includes an ethylenicallyunsaturated elastomer. The elastomer compound may also include more thanone ethylenically unsaturated elastomer. The ethylenically unsaturatedelastomer may be crosslinked to various degrees of crosslinking, e.g.,to various crosslinking densities, at various stages of the method 10(FIG. 1).

The ethylenically unsaturated elastomer may be, for example, anunsaturated rubber or a diene polymer or copolymer. Nonlimiting examplesof suitable diene monomers that may be used in preparing such elastomersinclude 1,3-butadiene, isoprene, 1,3-pentadiene (piperylene),2,3-dimethyl-1,3-butadiene, 1-phenyl-1,3-butadiene, 1,3-hexadiene,dicylopentadiene, thylidene norborene, and vinyl norborene. Nonlimitingexamples of suitable co-monomers that may be used with these includeethylene, propylene, and aromatic vinyl compounds like styrene.

Nonlimitng examples of suitable unsaturated rubbers include naturalrubbers (NR), synthetic rubbers, and mixtures of natural rubbers andsynthetic rubbers such as balata, gutta-percha, acrylate-butadienerubber (ABR), bromo-isobutylene-isoprene rubber (BIIR), butadiene rubber(BR), chloro-isoprene-isoprene rubber (CIIR), chloroprene rubber (CR),ethylene-propylene-diene rubber (EPDM), ethylene-propylene rubber (EPM),guayule rubber (GR), isobutylene-isoprene rubber (IIR), polyisobutylenerubber (IM), synthetic isoprene rubber (IR), acrylonitrile-butadienerubber (NBR), acrylonitrile-chloroprene rubber (NCR),acrylonitrile-isoprene rubber (NIR), vinylpyridine-styrene-butadienerubber (PSBR), styrene-butadiene rubber (SBR), styrene-chloroprenerubber (SCR), styrene-butadiene-styrene block copolymers (SBS),styrene-ethylene-butadiene-styrene block copolymers (SEBS),styrene-isoprene rubber (SIR), styrene-isoprene-styrene (SIS),vinylpyridine-butadiene rubber (VPBR),carboxylic-acrylonitrile-butadiene rubber (XNBR). These, as well as anyother diene-containing elastomers, may be used in any combination.

In one non-limiting embodiment that is particularly suitable for formingthe core 14 (FIG. 4) of the golf ball 112 (FIG. 4), the unsaturatedrubber may be a high 1,4-cis-polybutadiene rubber having at least about60%, preferably at least about 80%, more preferably at least about 90%,and most preferably at least about 95%, 1,4-cis content. In anothernon-limiting embodiment, the unsaturated rubber may be a low1,4-cis-polybutadiene rubber having at most about 50% 1,4-cis content.In another non-limiting embodiment, the unsaturated rubber may be a high1,4-trans-polybutadiene rubber having at least about 60%, preferably atleast about 70%, such as 75% or 80%, more preferably at least about 90%,and most preferably at least about 95%, 1,4-trans content. In yetanother non-limiting embodiment, the unsaturated rubber may be a low1,4-trans-polybutadiene rubber having less than about 40% 1,4-transcontent. Alternatively, the unsaturated rubber may be a high 1,2-vinylpolybutadiene rubber having at least about 40%, such as 50% or 60%, andpreferably at least about 70%, 1,2-vinyl content. In anothernon-limiting embodiment, the unsaturated rubber may be a low 1,2-vinylpolybutadiene rubber having at most about 30%, preferably at most about20%, and more preferably at most about 15%, such as about 10%, about 5%,or about 2%, 1,2-vinyl content.

In addition, the polybutadiene rubber may have any combination of1,4-cis-, 1,4-trans-, and vinyl structures or content, such as having a1,4-trans-content greater than a 1,4-cis-content or a 1,2-vinyl content;having a 1,4-cis-content greater than a 1,4-trans-content or a 1,2-vinylcontent; or having a 1,2-vinyl content greater than a 1,4-cis-content ora 1,4-trans-content. Further, combinations of more than one of theaforementioned unsaturated rubbers may be selected to provide desirablephysical, chemical, or performance characteristics of the article 12(FIG. 2) formed from the elastomer compounds, such as the golf ball 112(FIG. 4), including the core 14 (FIG. 4), the center 16 (FIG. 4), or oneor more intermediate layers 18 (FIG. 4).

In various embodiments a preferred ethylenically unsaturated elastomeris high 1,4-cis-polybutadiene rubber.

B. Monomer

In some embodiments particularly useful for forming the core 14 (FIG. 4)of the golf ball 112 (FIG. 4), the elastomer compound may also includean ethylenically-unsaturated monomer. For example, the elastomercompound may further include an unsaturated carboxylic acid or a metalsalt of the unsaturated carboxylic acid, which may effect crosslinkingof components during partially crosslinking 20 (FIG. 1). The elastomercompound may also include more than one unsaturated carboxylic acid ormetal salt of the unsaturated carboxylic acid.

The unsaturated carboxylic acid or the metal salt of the unsaturatedcarboxylic acid may have one or more ethylenic unsaturations. Suitableunsaturated carboxylic acids may include α,β-ethylenically unsaturatedacids or internally unsaturated acids or anhydrides having 3 to 30carbon atoms, such as acrylic acid, methacrylic acid, crotonic acid,maleic acid, fumaric acid, oleic acid, linoleic acid, erucic acid,maleic acid, and maleic anhydride.

Suitable metal salts of the unsaturated carboxylic acid may includeGroup I alkali metal salts, Group II alkaline earth metal salts,transition metal salts, or more specifically, magnesium salts, zincsalts, calcium salts, cobalt salts, iron salts, titanium salts, nickelsalts, manganese salts, aluminum salts, sodium salts, and copper salts.

Specific examples of preferable unsaturated carboxylic acids or metalsalts of the unsaturated carboxylic acids may include zinc diacrylate,magnesium diacrylate, calcium diacrylate, zinc dimethacrylate, magnesiumdimethacrylate, calcium dimethacrylate, zinc dioleate, magnesiumdioleate, calcium dioleate, zinc erucicate, magnesium erucicate, calciumerucicate, zinc maleate, magnesium maleate, calcium maleate, andcombinations thereof.

Further, the unsaturated carboxylic acid or the metal salt of theunsaturated carboxylic acid may be present in the elastomer compound inan amount up to at most about 80 parts by weight based on 100 parts byweight of the ethylenically unsaturated elastomer. For example, theunsaturated carboxylic acid or the metal salt of the unsaturatedcarboxylic acid may preferably be present in the elastomer compound inan amount of from at least about 15 parts by weight to at most about 60parts by weight based on 100 parts by weight of the ethylenicallyunsaturated elastomer. More preferably, the unsaturated carboxylic acidor the metal salt of the unsaturated carboxylic acid may be present inthe elastomer compound in an amount of from at least about 15 parts byweight to at most 40 parts by weight based on 100 parts by weight of theethylenically unsaturated elastomer.

In one non-limiting embodiment particularly suitable for the formationof golf ball cores 14 (FIG. 4), the unsaturated carboxylic acid or themetal salt of the unsaturated carboxylic acid may be zinc diacrylate orzinc dimethacrylate.

C. First Free Radical Initiator and Second Free Radical Initiator

Referring again to the method 10 (FIG. 1), the elastomer compound alsoincludes a first free radical initiator and a second free radicalinitiator. The elastomer compound may also include more than one firstfree radical initiator or more than one second free radical initiator.The first free radical initiator initiates partial crosslinking of theelastomer compound, and the second free radical initiator initiatesfurther crosslinking 22 (FIG. 1) of the precursor compound.

The first free radical initiator and the second free radical initiatormay initiate crosslinking of the ethylenically unsaturated elastomer atdifferent temperatures, i.e., at the first crosslinking temperature andat the second crosslinking temperature that is higher than the firstcrosslinking temperature, respectively. As such, the elastomer compoundincluding the ethylenically unsaturated elastomer is partiallycrosslinked at about the first crosslinking temperature, i.e., acomparatively lower temperature, and is further crosslinked at about thesecond crosslinking temperature, i.e., a comparatively highertemperature. Therefore, the first free radical initiator may becharacterized as a comparatively lower-temperature free radicalinitiator. In contrast, the second free radical initiator may becharacterized as a comparatively higher-temperature free radicalinitiator. Further, the second free radical initiator may not initiatepartial crosslinking of the elastomer compound in any significant extentduring a first stage of the method 10 (FIG. 1), but may only initiatefurther crosslinking 22 (FIG. 1) of the precursor compound at a secondstage of the method 10.

In a first relationship between the first and second free radicalinitiators, the first free radical initiator may have a half-life offrom about 0.2 minutes to about 5 minutes at the first crosslinkingtemperature, and the second free radical initiator may have a half-lifeof from about 0.2 minutes to about 5 minutes at the second crosslinkingtemperature, with the second crosslinking temperature being higher thanthe first crosslinking temperature by at least about 30° C. In somenon-limiting embodiments, the first free radical initiator may have ahalf-life at the first crosslinking temperature of from about 0.5minutes to about 4 minutes or from about 1 minute to about 3 minutes. Inthese or other embodiments, the second free radical initiator may have ahalf-life at the second crosslinking temperature of from about 0.5minutes to about 4 minutes or from about 1 minute to about 3 minutes.Further, the second crosslinking temperature may be higher than thefirst crosslinking temperature by at least about 35° C. or at leastabout 45° C. or at least about 50° C. or at least about 55° C. or atleast about 60° C. or at least about 65° C. or at least about 70° C. Invarious embodiments, the second crosslinking temperature may be higherthan the first crosslinking temperature by from about 30° C. or about35° C. or about 40° C. to about 90° C. or to about 95° C. or to about100° C., or preferably from about 40° C. to about 90° C. or from about40° C. to about 85° C. or from about 45° C. to about 85° C. or fromabout 40° C. to about 80° C. or from about 45° C. to about 80° C. orfrom about 45° C. to about 75° C. or from about 50° C. to about 90° C.or from about 50° C. to about 85° C. or from about 50° C. to about 80°C. or from about 50° C. to about 75° C.

Instead of or in addition to the initiator half-lives at the respectivecrosslinking temperatures and the difference between the first andsecond crosslinking temperatures just described, there may be a secondrelationship between the first and second initiators such that the firstfree radical initiator has a one-minute half-life temperature that is atleast about 30° C. lower than the second free radical initiator'sone-minute half-life temperature, and in various embodiments the firstfree radical initiator's one-minute half-life temperature can be atleast about 35° C. lower, or at least about 40° C. lower, or at leastabout 45° C. lower, or at least about 50° C. lower, or at least about55° C. lower, or at least about 60° C. lower, or at least about 65° C.lower, or at least about 70° C. lower, or at least about 75° C. lower,or at least about 80° C. lower than the second free radical initiator'sone-minute half-life temperature. In these embodiments, the firstcrosslinking temperature may be from about 20° C. lower to about 20° C.higher than the first one-minute half-life temperature and the secondcrosslinking temperature may be from about 20° C. lower to about 20° C.higher than the second one-minute half-life temperature. In exampleembodiments, the first crosslinking temperature may be from about 10° C.lower to about 10° C. higher than the first one-minute half-lifetemperature or from about 5° C. lower to about 5° C. higher than thefirst one-minute half-life temperature, and the second crosslinkingtemperature may independently be from about 10° C. lower to about 10° C.higher than the second one-minute half-life temperature or from about 5°C. lower to about 5° C. higher than the second one-minute half-lifetemperature. In particular embodiments of the second relationshipbetween the first and second initiators, the first initiator'sone-minute half-life temperature may be at least about 120° C. and atmost about 170° C., preferably at least about 130° C. and at most about155° C., or at least about 135° C. and at most about 150° C., or at mostabout 145° C., while, the second initiator's one-minute half-lifetemperature may be at least about 185° C. and at most about 260° C.,preferably at least about 190° C. and at most about 250° C., or at leastabout 200° C. and at most about 250° C., or at least 210° C. and at most250° C., or at most about 230° C.

The first and second initiators are preferably selected so that thefirst crosslinking temperature may be at least about 100° C. and at mostabout 190 C. For example, the first crosslinking temperature may be atleast about 110° C. and at most about 190° C., or at least about 110° C.and at most about 180° C., or at least about 120° C. and at most about180° C., or at least about 130° C. and at most about 180° C., or atleast about 130° C. and at most about 170° C., or at least about 150° C.and at most about 170° C. It should be noted that the heat of the firstcrosslinking reaction may cause the temperature to rise from the nominalfirst crosslinking temperature to which the elastomer compound isheated. The temperature during the first crosslinking step may beallowed to increase, but should remain at least about 30° C. lower thanthe second crosslinking temperature. Similarly, the first and secondinitiators are preferably selected so that the second crosslinkingtemperature may be at least about 160° C. and at most about 280° C. Forexample, the second crosslinking temperature may be at least about 170°C. and at most about 270° C., or at least about 180° C. and at mostabout 260° C., or at least about 190° C. and at most about 250° C., orat least about 200° C. and at most about 240° C., or at least about 210°C. and at most about 240° C.

The first free radical initiator and the second free radical initiatormay each be organic peroxides or azo compounds and, together with ioniccrosslinkings effected by the optional unsaturated carboxylic acid ormetal salt of the unsaturated carboxylic acid, may provide articles 12(FIG. 2) formed from the elastomer compound with improvedheat-resistance, flexibility, softness, resilience, and compression set.

Suitable organic peroxides may include, but are not limited to, dialkylorganic peroxides, diacyl organic peroxides, peroxyketal organicperoxides, peroxyester organic peroxides, peroxydicarbonates, andperoxymonocarbonates. More specifically, suitable organic peroxidesinclude, but are not limited to, di-t-amyl peroxide; di-t-butylperoxide; t-butyl cumyl peroxide; dicumyl peroxide;di(2-methyl-1-phenyl-2-propyl) peroxide;t-butyl-2-methyl-1-phenyl-2-propyl peroxide;di(t-butylperoxy)-diisopropylbenzene; benzoyl peroxide;1,1-di(t-butoxy)-3,3,5-trimethyl cyclohexane;3,3,5,7,7-pentamethyl-1,2,4-trioxepane; cumyl hydroperoxide; t-butylhydroperoxide; 2,5-dimethyl-2,5-di(t-butylperoxy) hexane;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne;2,5-dimethyl-2,5-di(benzoylperoxy)hexane;2,2′-bis(t-butylperoxy)-di-iso-propylbenzene; n-butyl4,4-bis(t-butyl-peroxy)valerate; t-butyl perbenzoate; benzoyl peroxide;n-butyl 4,4′-bis(butylperoxy) valerate; t-amyl perbenzoate;α,α-bis(t-butylperoxy)diisopropylbenzene; and combinations thereof thatsuit the parameters for the first and second free radical initiators ina particular embodiment.

In one non-limiting embodiment, the first free radical initiator may bea first organic peroxide or a first azo compound, and the second freeradical initiator may be a second organic peroxide or a second azocompound that is different from the first organic peroxide or the firstazo compound, respectively. The first free radical initiator and thesecond free radical initiator are different from one another. Forexample, the first free radical initiator may be dibenzoyl peroxide or1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, and the second freeradical initiator may be di-t-butyl peroxide, cumyl hydroperoxide,t-butyl hydroperoxide, or 3,3,5,7,7-pentamethyl-1,2,4-trioxepane.

Suitable azo compounds may include, but are not limited to,azobisisobutyronitrile (AIBN); 1,1′-azobis(cyclohexanecarbonitrile)(ABCN); 2,2′-azodi(2-methylbutyronitrile) (AMBN);2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride;2,2′-azobis[2-(2-imidazolin-2-yl)propane]disulfate dehydrate;2,2′-azobis(2-methylpropionamidine)dihydrochloride;2,2′-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate;2,2′-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}dihydrochloride;2,2′-azobis[2-(2-imidazolin-2-yl)propane];2,2′-azobis(1-imino-1-pyrrolidino-2-ethylpropane)dihydrochloride;2,2′-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethl]propionamide};2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide]; and combinationsthereof.

The first free radical initiator and the second free radical initiatormay be present in the elastomer compound in combination in an amount ofat least about 0.1 part by weight and at most about 20 parts by weightbased on 100 parts by weight of the ethylenically unsaturated elastomer.For example, the first free radical initiator and the second freeradical initiator may preferably be present in combination in theelastomer compound in an amount of at least about 0.1 part by weight andat most about 15 parts by weight based on 100 parts by weight of theethylenically unsaturated elastomer. At amounts less than about 0.1 partby weight or greater than about 10 parts by weight based on 100 parts byweight of the ethylenically unsaturated elastomer the ethylenicallyunsaturated elastomer may not be sufficiently crosslinked duringpartially crosslinking 20 (FIG. 1), over-crosslinked during furthercrosslinking 22 (FIG. 1), or the elastomer compound may be poorlyformed.

The first free radical initiator may be present in the elastomercompound in an amount of at most about 40 parts by weight based on 100parts by weight of a total amount of the first free radical initiatorand the second free radical initiator in combination. For example, thefirst free radical initiator may be present in the elastomer compound inan amount of from at least about 2 parts by weight and at most about 40parts by weight based on 100 parts by weight of the total amount of thefirst free radical initiator and the second free radical initiator. Invarious embodiments, the first free radical initiator may be present inthe elastomer compound in an amount of from at least about 5 parts byweight to at most about 40 parts by weight, or from at least about 2parts by weight to at most about 35 parts by weight, or from at leastabout 5 parts by weight to at most about 35 parts by weight, or from atleast about 8 parts by weight to at most about 35 parts by weight, orfrom at least about 10 parts by weight to at most about 30 parts byweight, or from at least about 10 parts by weight to about 30 parts byweight, or from at least about 5 parts by weight to at most about 25parts by weight, or from at least about 8 parts by weight to about 25parts by weight, based on 100 parts by weight of the total amount of thefirst free radical initiator and the second free radical initiator. Inanother example, the first free radical initiator may be present in theelastomer compound in an amount of from at least about 5 parts by weightand at most about 20 parts by weight based on 100 parts by weight of thetotal amount of the first free radical initiator and the second freeradical initiator.

D. Third Free Radical Initiator

The elastomer compound may optionally include a third free radicalinitiator. When included, the third free radical initiator may alsoinitiate partial crosslinking of the elastomer compound, but mayinitiate partial crosslinking at a lower temperature than that of thefirst free radical initiator. That is, the first free radical initiator,the second free radical initiator, and the third free radical initiatormay each initiate crosslinking of the elastomer compound at differenttemperatures, i.e., at the first crosslinking temperature, the secondcrosslinking temperature, and a third crosslinking temperature,respectively.

More specifically, the third free radical initiator initiates partialcrosslinking of the elastomer compound at the third crosslinkingtemperature, then the resulting partially crosslinked elastomer compoundis heated to the first crosslinking temperature at which furthercrosslinking initiated by the first initiator produces the precursorcompound as already described. The third free radical initiator may bepresent in the elastomer compound to introduce partial crosslinking ofthe elastomer compound at a comparatively lower third crosslinkingtemperature than the first crosslinking temperature and, in combinationwith the first free radical initiator at the first crosslinkingtemperature, impart sufficient rigidity to the precursor compound sothat the precursor compound may maintain a desired shape, such as, forexample, a half shell (not shown) for the golf ball 112 (FIG. 4).

The third free radical initiator may have a half-life of from about 0.2minutes to about 5 minutes at the third crosslinking temperature, or ahalf-life of from about 0.5 minutes to about 4 minutes or from about 1minute to about 3 minutes at the third crosslinking temperature.Further, the third crosslinking temperature may be less than the firstcrosslinking temperature by at least about 20° C., or by at least about25° C., or by at least about 30° C., or by at least about 35° C.Additionally or alternatively, the third free radical initiator may havea one-minute half-life temperature that is lower than the firstinitiator's one-minute half-life temperature, for example by at leastabout 20° C., or by at least about 25° C., or by at least about 30° C.,or by at least about 35° C. In specific examples, the third initiatormay have a one-minute half-life temperature of at least about 60° C. orat least about 65° C. or at least about 70° C. or at least about 75° C.and at most about 120° C. or at most about 110° C. or at most about 100°C. or at most about 90° C. For example, the third initiator may have aone-minute half-life temperature of from about 65° C. to about 90° C. orfrom about 70° C. to about 100° C.

In specific examples, depending on the third free radical initiator andfirst free radical initiator selected, the third crosslinkingtemperature may be from about 50° C., about 55° C., or about 60° C. toat most about 120° C., about 110° C., or about 100° C.

The third free radical initiator may also be selected to provide theelastomer compound with excellent heat stability, flexibility,resilience, and compression set. The third free radical initiator mayalso be selected from azo compounds or organic peroxides such as, butnot limited to, dialkyl organic peroxides, diacyl organic peroxides,peroxyketal organic peroxides, peroxyester organic peroxides,peroxydicarbonates, and peroxymonocarbonates. Further, the third freeradical initiator is different from the first free radical initiator andthe second free radical initiator.

When included, the third free radical initiator may be present in theelastomer compound in an amount of at most about 25 parts by weightbased on 100 parts by weight of a total amount of the first free radicalinitiator, the second free radical initiator, and the third free radicalinitiator in combination. For example, the third free radical initiatormay be present in the elastomer compound in an amount of from at leastabout 1 part by weight or about 2 parts by weight and at most about 25parts by weight or about 20 parts by weight based on 100 parts by weightof the total amount of the first free radical initiator, the second freeradical initiator, and the third free radical initiator. Morepreferably, the third free radical initiator may be present in theelastomer compound in an amount of from at least about 2 parts by weightand at most about 20 parts by weight, from at least about 3 parts byweight and at most about 20 parts by weight, from at least about 2 partsby weight and at most about 15 parts by weight, from at least about 3parts by weight and at most about 15 parts by weight, based on 100 partsby weight of the total amount of the first free radical initiator, thesecond free radical initiator, and the third free radical initiator.

E. Additives

The physical properties of the cured elastomer may also be modified byincluding one or more additives in the elastomer compound. That is, theelastomer compound may include one or more additives such as, but notlimited to, processing agents, anti-oxidants, ultraviolet stabilizers,pigments, plasticizers, rheology modifiers (such as nano-particleshaving comparatively high aspect ratios, nano-clays, nano-carbon,graphite, nano-silica, and the like), and combinations thereof.

The physical properties of the golf ball 112 (FIG. 4) or the core 14(FIG. 4) or other article made with the cured elastomer may also bemodified by including a filler component in the elastomer compound. Theelastomer compound may include a filler component such as, but notlimited to, clay, talc, asbestos, graphite, glass, mica, calciummetasilicate, barium sulfate, zinc sulfide, aluminum hydroxide,silicates, diatomaceous earth, carbonates (such as calcium carbonate,magnesium carbonate and the like), metals (such as titanium, tungsten,zinc, aluminum, bismuth, nickel, molybdenum, iron, copper, brass, boron,bronze, cobalt, beryllium, and alloys of these), metal oxides (such aszinc oxide, iron oxide, aluminum oxide, titanium oxide, magnesium oxide,zirconium oxide and the like), particulate synthetic plastics (such ashigh molecular weight polyethylene, polypropylene, polystyrene,polyethylene ionomeric resins, polyamide, polyester, polyurethane,polyimide, and the like), particulate carbonaceous materials (such ascarbon black and the like), as well as cotton flock, cellulose flock,cellulose pulp, leather fiber, and combinations of any of the above.Non-limiting examples of heavy-weight filler components that may be usedto increase the specific gravity of the cured elastomer may includetitanium, tungsten, aluminum, bismuth, nickel, molybdenum, iron, steel,lead, copper, brass, boron, boron carbide whiskers, bronze, cobalt,beryllium, zinc, tin, metal oxides (such as zinc oxide, iron oxide,aluminum oxide, titanium oxide, magnesium oxide, and zirconium oxide),metal sulfates (such as barium sulfate), metal carbonates (such ascalcium carbonate), and combinations thereof. Non-limiting examples oflight-weight filler components that may be used to decrease the specificgravity of the cured elastomer may include particulate plastics, hollowglass spheres, ceramics, and hollow spheres, regrinds, or foams thereof.Such fillers may be used, for example, in golf balls to affect theweight or moment of inertia of the golf ball. For example, withreference to FIG. 4, any of the center 16 or intermediate layers 18, 19forming the core of golf ball 112 may be made from the presentdynamically crosslinked thermoplastic materials in which the rubberdomains include one or more fillers selected to provide a certain weightor weight distribution to the golf ball 112.

Typical levels of these and other fillers include from about 10 phr to100 phr or higher (where “phr” indicates parts by weight based on 100parts of the elastomer). In various embodiments, the compositions maycontain 10-80, 30-70, 40-60, or 50-60 phr filler. In variousembodiments, the elastomer compound comprises a silica filler. Typicallevels of silica filler include from about 10 phr to 100 phr or higher.In various embodiments, the elastomer compound may contain 10-80, 30-70,10-60, 40-60, 50-60, or 35-60 phr filler.

The elastomer compound may include any of a wide variety of black,white, or colored pigments.

Particularly in the case of a rubber elastomer, the elastomer mayoptionally be compounded with a process oil to facilitate bothcompounding and processing. Process oils may come from petroleumsources, i.e. oils derived from plant or animal sources. The petroleumprocess oils may be hydrotreated to remove at least a large portion ofthe aromatic compounds. Petroleum-based oils can be selected from thegroup consisting of paraffinic oils, naphthenic oils, and aromatic oils.The non-petroleum-based oils may contain a sufficient level anddistribution of fatty acid side chains to partially incorporate into therubber composition at low levels or to act as internal plasticizers athigher levels. The oils derived from plant or animal sources can beclassified by their iodine number. Plant- and animal-derived oils maycontain double bonds, and each double bond can react with one iodinemolecule. The iodine number, defined as the number of grams of iodinetaken up by 100 grams of oil, gives a rough measure of the number ofdouble bonds in an oil. The oil may have an iodine number of greaterthan 50 and, preferably, greater than 60. During crosslinking the doublebonds are available for reaction with the unsaturated elastomermolecules. In another aspect, these oils are triglycerides of one ormore unsaturated fatty acids. Such a plant- or animal-derived oil iscapable of effectively crosslinking an unsaturated elastomer duringcrosslinking if the oil molecule contains a double bond on two or moreof the three fatty acid side chains in an oil molecule. Preferred oilsmay have at least 50% of the fatty acid side chains with one or moresites of unsaturation. In this way, the unsaturated oils can facilitateprocessing of the rubber during the compounding phase and can beincorporated into the rubber network during the curing phase to enhancethe physical properties of the rubber composition and prevent blooming.

In some embodiments the elastomer compound contains less than 5 phr(parts by weight per hundred parts of elastomer) of the process oil,preferably less than or equal to 3 phr. The elastomer composition maycontain from about 0.1 to about 5 phr of vegetable oil. In otherembodiments, the elastomer compounds contain a maximum of 3 phrvegetable oil, or less than 3 phr. In other embodiments, the elastomercompounds may contain from 0.1 to 2 phr vegetable oil. Non-limitingexamples of vegetable oils include peanut oil, sunflower oil, cottonseedoil, linseed oil, soybean oil, rapeseed oil, sesame oil, safflower oil,poppy seed oil, tung oil, wheat oil, olive oil, palm oil, coconut oil,corn oil, palm-kernel oil, castor oil, cocoa butter, cocoa oil, andmixtures thereof. Castor oil has unique chemistry in that it is the onlysource of an 18 carbon hydroxylated fatty acid with one double bond(12-hydroxyoleic acid or ricinoleic acid). This fatty acid consistentlycomprises about 90% of castor oil. The presence of hydroxyl groupsprovides this oil with advantages, especially in predominantly saturatedrubbers such as butyl (IIR) and halogenated butyl rubbers (BIIR, CIIR).Castor oil can also be used in more polar rubber compounds such ashalogenated rubbers. This is especially advantageous, since traditionalpetroleum oils have limited solubility in these types of rubbers.

The ethylenically unsaturated elastomer, first free radical initiator,second free radical initiator, optional third free radical initiator,optional unsaturated carboxylic acid or metal salt of the unsaturatedcarboxylic acid, and optional additives may be compounded together toform the elastomer compound. For example, the components may be mixedtogether in a continuous mixer or a batch mixer, e.g., an intermeshingrotor mixer, such as an Intermix mixer, an extruder (e.g., a twin screwextruder), a tangential rotor mixer such as a Banbury mixer, or a tworoll mill. The mixer may blend the components together via a single stepor multiple steps, and may mix the components via dispersive mixing ordistributive mixing to form the resulting elastomer compound.

The resulting elastomer compound may be a blend of comparatively highmolecular weight components and comparatively low molecular weightcomponents, and may be a generally flowable compound having a viscositysuitable for handling and further processing. Comparatively highermolecular weight components may increase the solidity of the elastomercompound, and comparatively lower molecular weight components mayenhance the fluidity of the elastomer compound.

Partially Crosslinking at the First Crosslinking Temperature

Referring again to FIG. 1, the method 10 of forming the cured elastomerincludes partially crosslinking 20 the elastomer compound at the firstcrosslinking temperature to form the precursor compound. The method 10also includes further crosslinking 22 the precursor compound at thesecond crosslinking temperature.

For the method 10 (FIG. 1), partially crosslinking 20 (FIG. 1) mayinclude heating 30 (FIG. 3) the elastomer compound to about the firstcrosslinking temperature for from about 0.5 minute to about 15 minutes.For example, partially crosslinking 20 may include curing the elastomercompound at the first crosslinking temperature for from about 0.5 minuteor from at least about 1 minute or from at least about 2 minutes or fromat least about 3 minutes or at least about 4 minutes or at least about 5minutes to at most about 15 minutes or at most about 13 minutes or atmost about 10 minutes, or at most about 7 minutes, or at most about 6minutes. In other examples, partially crosslinking 20 may include curingthe elastomer compound at the first crosslinking temperature for fromabout 0.5 minute or for at least about 1 minute or at least about 2minutes to at most about 3 minutes.

In one example, partially crosslinking 20 (FIG. 1) may include curingthe elastomer compound at the first crosslinking temperature for fromabout 0.5 to about 5 minutes or from about 0.5 to about 3 minutes.

After partially crosslinking 20 (FIG. 1), the resulting precursorcompound is thermoplastic, and is further crosslinkable. That is, theprecursor compound remains moldable. Further, the precursor compound mayhave a first crosslinking density. As used herein, “crosslinkingdensity” refers to an average number of chain segments betweencrosslinks per unit volume of the precursor compound or cured elastomer.That is, crosslinking density refers to a concentration of crosslinkswithin the precursor compound or cured elastomer. In contrast, afterfurther crosslinking 22 (FIG. 1), the cured elastomer may be fullycured, and may have a final crosslinking density. In particular,partially crosslinking 20 may include curing the elastomer compound sothat the first crosslinking density is at most about 40% of the finalcrosslinking density. For example, the first crosslinking density of theprecursor compound after partially crosslinking 20 may be from about 1%to about 40%, or from about 2% to about 40%, or from about 2% to about30%, or from about 5% to about 30%, or from about 5% to about 20%, orfrom about 10% to about 30%, or from about 20% to about 30% of the finalcrosslinking density. That is, the elastomer compound is partiallycrosslinked at the first crosslinking temperature to a firstcrosslinking density that is at most about 40% of the first crosslinkingdensity. In other examples, the first crosslinking density of theprecursor compound after partially crosslinking 20 may be from about 1%to about 20%, or from about 2% to about 20%, or from about 2% to about10%, or from about 5% to about 20%, or from about 5% to about 10% of thefinal crosslinking density.

The resulting precursor compound may have a non-fluid physical form, andmay have sufficient mechanical integrity to maintain a desired shape,even though the precursor compound is thermoplastic. That is, theprecursor compound may have a physical form that is suitable forhandling and further processing, including sufficient crosslinking so asto hold a desired shape. The precursor compound has a relatively lowerdegree of crosslinking compared to the final completely cured elastomercompound.

A. Molding the Elastomer Compound

With continued reference to FIG. 1, the method 10 may further include,concurrent to partially crosslinking 20, molding 42 the elastomercompound in a cavity defined by a mold to form the precursor compound.That is, the elastomer compound may be partially crosslinked within thecavity of the mold. For example, the elastomer compound may be fed to aninjection molding device (not shown), and advanced through the injectionmolding device by one or more screws (not shown) towards the cavity ofthe mold. As the one or more screws advance the elastomer compoundthrough the injection molding device, the elastomer compound may beheated to the about the first crosslinking temperature and injected intothe cavity of the mold. As such, the elastomer compound may be partiallycrosslinked within the cavity of the mold to thereby form the precursorcompound. For this embodiment, the precursor compound may be formed intoa desired shape, such as a preform.

In another embodiment, molding 42 may include compression molding 32(FIG. 3) the elastomer compound within the cavity defined by the mold.For example, the mold may include a first portion and a second portionmatable with the first portion to define the cavity between them. Theelastomer compound may be heated to about the first crosslinkingtemperature and disposed within the first portion of the open, heatedcavity of the mold, and the second portion may mate with the firstportion to seal off the cavity. The elastomer compound may be partiallycrosslinked within the cavity of the mold to thereby form the precursorcompound.

B. Extruding the Elastomer Compound

Alternatively, in another embodiment described with continued referenceto FIG. 1, the method 10 may further include, partially crosslinking 20the elastomer compound 20 in an extruder and then extruding 34 thepartially-crosslinked elastomer compound as strands through a pluralityof openings defined by a die and cut to form the plurality of pellets.The elastomer, initiators, and other components may be fed into theextruder, for example by a hopper or other port or ports and advancedthrough the extruder by one or more screws with mixing and kneading ofthe components by the screws, then extruded through an opening oropenings in a die at the downstream end of the extruder. As the one ormore screws advance the mixed elastomer compound through the extruder,the elastomer compound may be heated to the first crosslinkingtemperature to partially crosslink the elastomer within the extruder toform a precursor compound that is extruded through a die at the end ofthe extruder. The elastomer compound may also be made in otherequipment, then introduced into the extruder for partial crosslinked atthe first crosslinking temperature. The die may, for example, have aplurality of openings and the extrudate may be extruded as filamentsthat are cooled to solidify the precursor compound (e.g., in a waterbath) and pelletized by cutting, e.g., with a rotary cutter, intopellets for subsequent molding at the second crosslinking temperature toform the cured elastomer article. For example, the precursor compoundpellets may be subsequently fed to an injection molding device or moldedin a compression molding device. Alternatively, the pellets could alsobe formed by an underwater die face pelletizer.

Advantageously, the resulting plurality of pellets formed from theprecursor compound may have sufficient mechanical integrity such thatthe plurality of pellets may not fuse together, but may instead remainseparated as individual pellets. As such, the plurality of pellets maybe optionally mixed with other feedstock or subsequently processed,e.g., molded by injection or compression, into a desired shape.

In an alternative embodiment, the elastomer, initiators, and othercomponents may be compounded before being introduced into the extruder.For example, the compounding may take place in a different extruder, atwo-roll mill, or other equipment useful for mixing such materials.

In an alternative embodiment, the partially-crosslinked elastomercompound may be extruded in a different shape, for example a sheet ortube or may be extruded into an injection mold where it is furthercrosslinked at a second crosslinking temperature.

Further Crosslinking at the Second Crosslinking Temperature

Referring again to the method 10 (FIG. 1), the method 10 also includesfurther crosslinking 22 (FIG. 1) the precursor compound at the secondcrosslinking temperature that is higher than the first crosslinkingtemperature or related to the one-minute half-life temperature of thesecond initiator as earlier described to thereby form the curedelastomer. Further crosslinking 22 (FIG. 1) in general adds to a totalnumber of crosslinks or covalent bonds of the elastomer, further curingthe precursor compound to thereby form the cured elastomer article. Thatis, further crosslinking 22 builds upon the partial crosslinkingpreviously effected at the first crosslinking temperature. The precursorcompound product of the first crosslinking temperature, subject to thefurther crosslinking 22, transitions to the cured elastomer at thesecond crosslinking temperature.

Further crosslinking 22 (FIG. 1) includes heating 30 (FIG. 3) theprecursor compound to the second crosslinking temperature for a periodof time, such as from about 1 minute to about 30 minutes. For example,further crosslinking 22 may include curing the precursor compound at thesecond crosslinking temperature for from about 1 to about 30 minutes, orfrom about 3 to about 30 minutes, or from at least about 3 minutes toabout 25 minutes, or from at least about 3 minutes to about 20 minutes,or from about 5 to about 30 minutes, or from at least about 5 minutes toabout 25 minutes, or from at least about 5 minutes to about 20 minutes,or from about 7 to about 30 minutes, or from at least about 7 minutes toabout 25 minutes, or from at least about 7 minutes to about 20 minutes,or from about 10 to about 30 minutes, or from at least about 10 minutesto about 25 minutes, or from at least about 10 minutes to about 20minutes.

After further crosslinking 22 (FIG. 1), the resulting cured elastomer isa thermoset, which may not be further crosslinkable. That is, the curedelastomer may have the final crosslinking density. Therefore, the method10 (FIG. 1) may be a dual-free radical initiator, dual-stage, dual-curetemperature process, and the cured elastomer may have any desired shape.That is, the cured elastomer may be substantially fully crosslinked orcured and may exhibit an as-molded shape or final form, or may be cut,ground, or shaved to a final shape or form.

Molding the Precursor Compound

With continued reference to FIG. 1, the method 10 may further include,concurrent to further crosslinking 22, molding 42 the precursor compoundin the cavity defined by the mold. For example, for embodiments in whichthe precursor compound is formed within the injection molding devicewhen the elastomer compound reaches about the first crosslinkingtemperature, the precursor compound may continue to advance through asecond portion of the injection molding device (not shown) towards thecavity of the mold. The precursor compound may be injected into thecavity and molded within the cavity to form the cured elastomer.

In another example, the precursor compound may be compression molded.For example, the precursor compound may be heated to about the secondcrosslinking temperature and disposed within the first portion of theopen, heated cavity of the mold, and the second portion may mate withthe first portion to seal off the cavity. As such, the precursorcompound may be further crosslinked within the cavity of the mold tothereby form the cured elastomer.

Alternatively, referring again to FIG. 1, the resulting plurality ofpellets formed from the precursor compound during extrusion may then besubsequently processed to form the cured elastomer. For example, furthercrosslinking 22 may include molding 42 the plurality of pellets withinthe cavity defined by the mold. In one embodiment, the precursorcompound in pelletized form may be further crosslinked via an injectionmolding device (not shown). For example, the precursor compound mayadvance through the injection molding device by one or more screwstowards the cavity of the mold. As the one or more screws advances theprecursor compound through the injection molding device, the precursorcompound may be injected into the cavity of the mold and heated to aboutthe second crosslinking temperature. As such, the precursor compound maybe further crosslinked within the cavity of the mold to thereby form thecured elastomer.

Alternatively, as shown in FIG. 1, the resulting plurality of pelletsformed during extruding 34 may then be subsequently compression moldedto form the cured elastomer. For example, further crosslinking 22 mayinclude compression molding 32 the plurality of pellets within thecavity defined by the mold and heating 30 (FIG. 3) the precursorcompound to about the second crosslinking temperature. That is, theprecursor compound may be further crosslinked by compression molding 32(FIG. 3) the precursor compound in pelletized form within the cavity ofthe mold. For example, the precursor compound may be heated to about thesecond crosslinking temperature and disposed within the first portion ofthe open, heated cavity of the mold, and the second portion may matewith the first portion to seal off the cavity. As such, the precursorcompound may be further crosslinked within the cavity of the mold tothereby form the cured elastomer.

Compounding the Third Free Radical Initiator

For embodiments in which the elastomer compound includes the optionalthird free radical initiator, the method 10 (FIG. 1) may furtherinclude, before partially crosslinking 20 (FIG. 1), compounding 26(FIG. 1) the first free radical initiator, the second free radicalinitiator, the elastomer (which may be an ethylenically unsaturatedelastomer), and the third free radical initiator to thereby form theelastomer compound. Likewise, for embodiments in which the elastomercompound includes the unsaturated monomer (e.g., unsaturated carboxylicacid or the metal salt of the unsaturated carboxylic acid), the method10 may further include, before partially crosslinking 20, compounding 26the first free radical initiator, the second free radical initiator, theoptional third free radical initiator, the ethylenically unsaturatedelastomer, and the unsaturated carboxylic acid or the metal salt of theunsaturated carboxylic acid to thereby form the elastomer compound. Forexample, the components may be mixed together in a continuous mixer or abatch mixer, e.g., an intermeshing rotor mixer, such as an Intermixmixer, a tangential rotor mixer such as a Banbury mixer, or a two rollmill. The mixer may blend the components together via a single step ormultiple steps, and may mix the components via dispersive mixing ordistributive mixing to form the resulting elastomer compound.

For these embodiments including the third free radical initiator,partially crosslinking 20 (FIG. 1) may include first curing theelastomer compound at the third crosslinking temperature. Therefore, forembodiments including the third free radical initiator, partiallycrosslinking 20 (FIG. 1) may include curing the elastomer compound atthe third crosslinking temperature for at most about 15 minutes. Forexample, partially crosslinking 20 may include curing the elastomercompound at the third crosslinking temperature for at least about 0.5minute or about 1 minute, or about 2 minutes, or about 3 minutes, orabout 4 minutes, or about 5 minutes and up to about 15 minutes, or up toabout 12 minutes, or up to about 10 minutes, or up to about 8 minutes.In other examples, partially crosslinking 20 may include curing theelastomer compound at the third crosslinking temperature for at leastabout 0.5 minute, or about 1 minute, or about 2 minutes up to about 6minutes, or up to about 5 minutes, or up to about 4 minutes.

The third crosslinking density may be from about 1% to about 50% of theof the first crosslinking density. For example, the third crosslinkingdensity may be from about 1% to about 40%, or from about 2% to about40%, or from about 2% to about 30%, or from about 5% to about 30%, orfrom about 5% to about 20%, or from about 10% to about 30%, or fromabout 20% to about 30% of the first crosslinking density. In otherexamples, the first crosslinking density of the precursor compound afterpartially crosslinking 20 may be from about 1% to about 20%, or fromabout 2% to about 20%, or from about 2% to about 10%, or from about 5%to about 20%, or from about 5% to about 10% of the first crosslinkingdensity.

For embodiments including the third free radical initiator, partiallycrosslinking 20 may also be a dual-free radical initiator process, i.e.,the third free radical initiator and the first free radical initiator; adual-stage process, i.e., partially crosslinking 20 at the thirdcrosslinking temperature and partially crosslinking 20 at the firstcrosslinking temperature; and a dual-cure temperature process, i.e., thethird crosslinking temperature and the first crosslinking temperature.

Molding

Referring now to FIG. 3, a method 110 of forming the golf ball 112 (FIG.4) includes partially crosslinking 20 the elastomer compound at thefirst crosslinking temperature to form the precursor compound. Theelastomer compound comprises the first free radical initiator, thesecond free radical initiator, and the ethylenically unsaturatedelastomer. The elastomer compound may also optionally include theunsaturated carboxylic acid or the metal salt of the unsaturatedcarboxylic acid. In addition, the elastomer compound may also optionallyinclude the third free radical initiator. The method 110 (FIG. 3) alsoincludes forming 122 (FIG. 3) a golf ball core or core component byfurther crosslinking 22 the precursor compound at the secondcrosslinking temperature to thereby form the cured elastomer.

B. Injection Molding

With continued reference to FIG. 3, the method 110 may further include,concurrent to partially crosslinking 20, injecting 28 the elastomercompound into a cavity defined by a mold. That is, the elastomercompound may be partially crosslinked within the cavity of the mold. Forexample, the elastomer compound may be fed to an injection moldingdevice (not shown), and advanced through the injection molding device byone or more screws (not shown) towards the cavity of the mold. As theone or more screws advance the elastomer compound through the injectionmolding device, the elastomer compound may be heated to the about thefirst crosslinking temperature and injected into the cavity of the mold.As such, the elastomer compound may be partially crosslinked within thecavity of the mold to thereby form the precursor compound. For thisembodiment, the precursor compound may be formed into a desired shape,such as a preform or one or more half shells that may subsequently mateto form the core center 16 or an intermediate layer 18, 19 of the golfball 112 (FIG. 4). For example, two half shells formed from theprecursor compound may be subsequently fused, for example, bycompression, into one or more intermediate layers 18, 19 (FIG. 4) of thegolf ball 112.

For the method 110 (FIG. 3), the precursor compound is subsequentlyprocessed to form the cured elastomer. By way of non-limiting examples,the method 110 may include processing the precursor compound viathermoforming, vacuum forming, injection molding, compression molding,cutting, stamping, grinding, and other forming processes.

For example, for embodiments in which the elastomer compound ispartially crosslinked within the injection molding device (not shown),further crosslinking 22 (FIG. 3) may include continuing to process theprecursor compound within the injection molding device. For example,further crosslinking 22 may include injecting 28 (FIG. 3) the precursorcompound into the cavity defined by the mold and heating 30 (FIG. 3) theprecursor compound to about the second crosslinking temperature. Thatis, the precursor compound may be further crosslinked within the cavityof the mold.

For example, the precursor compound may continue to travel through theinjection molding device, e.g., through a second portion of theinjection molding device, and advance through the injection moldingdevice via the one or more screws (not shown) towards the cavity of themold. As the one or more screws continue to advance the precursorcompound through the injection molding device, the precursor compoundmay be injected into the cavity of the mold and heated to the about thesecond crosslinking temperature. The precursor compound may be furthercrosslinked within the cavity of the mold to thereby form the curedelastomer.

B. Compression Molding

With continued reference to FIG. 3, in another embodiment, the method110 may include, concurrent to partially crosslinking 20, compressionmolding 32 the elastomer compound within the cavity defined by the mold.That is, the elastomer compound may be partially crosslinked within thecavity of the mold. For example, the mold may include a first portionand a second portion matable with the first portion to define the cavitytherebetween. The elastomer compound may be heated to about the firstcrosslinking temperature and disposed within the first portion of theopen, heated cavity of the mold, and the second portion may mate withthe first portion to seal off the cavity. As such, the elastomercompound may be partially crosslinked within the cavity of the mold tothereby form the precursor compound.

That is, as shown in FIG. 3, the resulting precursor compound formedduring compression molding 32 may then be subsequently processed to formthe cured elastomer. For example, further crosslinking 122 may includecompression molding 32 the precursor compound within the cavity definedby the mold and heating 30 the precursor compound to about the secondcrosslinking temperature. For example, the precursor compound may beheated to about the second crosslinking temperature and disposed withinthe first portion of the open, heated cavity of the mold, and the secondportion may mate with the first portion to seal off the cavity. As such,the precursor compound may be further crosslinked within the cavity ofthe mold to thereby form the cured elastomer. For this embodiment, thecured elastomer may be formed into the cured elastomer article.

C. Extruding

Alternatively, in another embodiment described with continued referenceto FIG. 3, the method 110 may further include, concurrent to partiallycrosslinking 20, extruding 34 the elastomer compound through a pluralityof openings defined by a die to thereby form a plurality of pelletsformed from the precursor compound. For example, the elastomer compoundmay be extruded through the plurality of openings and cut to form theplurality of pellets. In particular, the elastomer compound may beinjected into an extruder (not shown), and advanced through the extruderby one or more screws (not shown) towards the plurality of openings ofthe die. As the one or more screws advance the elastomer compoundthrough the extruder, the elastomer compound may be heated to the aboutthe first crosslinking temperature. As such, the elastomer compound maybe partially crosslinked within the extruder and extruded through theplurality of openings to thereby form the precursor compound inpelletized form. For this embodiment, the precursor compound may beformed into the plurality of pellets that may be subsequently fed to aninjection molding device or a compression molding device.

Advantageously, the resulting plurality of pellets formed from theprecursor compound may have sufficient mechanical integrity such thatthe plurality of pellets may not fuse together, but may instead remainseparated as individual pellets. As such, the plurality of pellets maybe optionally mixed with other feedstock or subsequently processed,e.g., molded by injection or compression, into one or more intermediatelayers 18, 19 (FIG. 4) or the center 16 (FIG. 4) of the golf ball 112(FIG. 4).

Referring again to FIG. 3, the resulting plurality of pellets formedfrom the precursor compound during extrusion may then be subsequentlyprocessed to form the cured elastomer. For example, further crosslinking22 may include injecting 28 the plurality of pellets into the cavitydefined by the mold and heating 30 the plurality of pellets to about thesecond crosslinking temperature. That is, the precursor compound inpelletized form may be further crosslinked via an injection moldingdevice (not shown). For example, the precursor compound may advancethrough the injection molding device by one or more screws towards thecavity of the mold. As the one or more screws advances the precursorcompound through the injection molding device, the precursor compoundmay be injected into the cavity of the mold and heated to about thesecond crosslinking temperature. As such, the precursor compound may befurther crosslinked within the cavity of the mold to thereby form thecured elastomer. For this embodiment, the cured elastomer may have anydesired shape, such as one or more half shells (not shown) that maysubsequently mate to form the golf ball 112 (FIG. 4). Two half shellsformed from the cured elastomer may be subsequently fused, for example,with heat or an adhesive, into one or more intermediate layers 18, 19(FIG. 4) or the center 16 of the golf ball 112.

Alternatively, as shown in FIG. 3, the resulting plurality of pelletsformed during extruding 34 may then be subsequently compression moldedto form the cured elastomer. For example, further crosslinking 22 mayinclude compression molding 32 the plurality of pellets within thecavity defined by the mold and heating 30 the precursor compound toabout the second crosslinking temperature. That is, the precursorcompound may be further crosslinked by compression molding 32 theprecursor compound in pelletized form within the cavity of the mold. Forexample, the precursor compound may be heated to about the secondcrosslinking temperature and disposed within the first portion of theopen, heated cavity of the mold, and the second portion may mate withthe first portion to seal off the cavity. As such, the precursorcompound may be further crosslinked within the cavity of the mold tothereby form the cured elastomer. For this embodiment, the curedelastomer may be formed into a desired shape, such as the center 16(FIG. 4) of the golf ball 112 (FIG. 4).

Golf Ball Manufacturing

Referring now to FIGS. 3 and 4, the method 110 (FIG. 3) also includesdisposing 36 (FIG. 3) the cover 24 (FIG. 4) on the outermostintermediate layer 19 (FIG. 4), such that the cover 24 surrounds theoutermost intermediate layer 19 to thereby form the golf ball 112 (FIG.4). For example, the cover 24 may also be formed by compression moldingor injection molding, and may include a first hemispherical half and asecond hemispherical half which may cooperate to surround the core 14.The cover 24 may have a plurality of dimples 26 and may be configured orarranged to affect a spin rate of the golf ball 112 during flight. Assuch, the cover 24 may be a comparatively thin, exterior structurallayer of the golf ball 112. The cover 24 may also include anon-structural layer, such as a coating, e.g., a brand marking, a colorcoat, or a clearcoat.

In general, the golf ball 112 may be formed through one or moreinjection molding or compression molding steps. For example, in oneconfiguration, the fabrication of a multi-layer golf ball 112 mayinclude: forming a center 16 through injection molding; compressionmolding a cold-formed or partially-crosslinked elastomer intermediatelayer 18 about the center 16; compression or injection molding a furtherintermediate layer 19 around intermediate layer 18; and forming a coverlayer 24 about the intermediate layer 19 though injection molding orcompression molding.

In certain embodiments, the center 16 may be made, for example bycompression or injection molding, from an elastomer compound bytwo-crosslinking temperature method. In certain embodiments, one or moreintermediate layers may be formed between the center 16 and theelastomer intermediate layer 18 and the ball then may or may not includean intermediate layer 19 or other intermediate layers around theintermediate layer 18. In other embodiments, cover layer 24 may beformed from the elastomer compound or partially-crosslinked elastomerinstead of or in addition to a center or intermediate layer that isformed from the elastomer compound or partially-crosslinked elastomer.

As schematically illustrated in FIGS. 5A & 5B, during the injectionmolding process used to form the center 16, two hemispherical dies 150,152 may cooperate to form a mold cavity 154 that may be filled with athermoplastic material 156 in a flowable state. The hemisphericalmolding dies 150, 152 may meet at a parting line 158. In oneconfiguration, a thermoplastic ionomer may be used to form the center16. Suitable thermoplastic ionomeric materials are commerciallyavailable, for example, from the E. I. du Pont de Nemours and Company.In particular embodiments, the center may be formed from a highlyneutralized thermoplastic ionomer composition in which the ionomer resinis formed by adding a sufficiently high molecular weight, monomeric,mono-functional organic acid or salt of organic acid to the acidcopolymer or ionomer so that the acid copolymer or ionomer can beneutralized, without losing processability, to a level above the levelthat would cause the ionomer alone to become non-melt-processable.

Once the material 156 is cooled to ambient temperature, it may hardenand be removed from the molding dies. Once the center 16 is formed andremoved from the mold, any molding flash may be removed using anycombination of cutting, grinding, sanding, tumbling with an abrasivemedia, and/or cryogenic deflashing. Following the deflashing, anadhesive or bonding agent may be applied to the outer surface of thecenter, such as through spraying, tumbling, and/or dipping.Additionally, one or more surface treatments may also be employed atthis stage, such as mechanical surface roughening, plasma treatment,corona discharge treatment, or chemical treatment to increase subsequentadhesion to intermediate layer 18. Nonlimiting, suitable examples ofadhesives and bonding agents that may be used include polymericadhesives such as ethylene vinyl acetate copolymers, two-componentadhesives such as epoxy resins, polyurethane resins, acrylic resins,polyester resins, and cellulose resins and crosslinkers therefor, e.g.,with polyamine or polycarboxylic acid crosslinkers for polyepoxidesresins, polyisocyanate crosslinkers for polyalcohol-functional resins,and so on; or siliane coupling agents or silane adhesives. The adhesiveor bonding agent may be used with or without a surface treatment such asmechanical surface roughening, plasma treatment, corona dischargetreatment, or chemical treatment.

Once any surface coatings/preparations are applied/performed (if any),the intermediate layer 18 may then be formed around the center 16, forexample, through a compression molding process. During compressionmolding, two hemispherical blanks of the elastomer compound or theprecursor compound may be press-fit around the center 16. Oncepositioned, a suitable die may apply heat and/or pressure to theexterior of the blanks to cure/crosslink the blanks while fusing themtogether in, for blanks of the elastomer compound, a two-stage cure atthe first and second crosslinking temperatures or, for blanks of theprecursor compound, the final crosslinking at the second crosslinkingtemperature. During the curing process, the application of heat and theapplied pressure may cause the elastomer material to conform to andadhere to the outer surface of the center 16.

FIGS. 6A-6D further illustrate an embodiment of a process that may beused to compression mold an intermediate layer 18 about the center 16.As shown in FIG. 6A, the intermediate layer may begin as piece ofelastomer compound 160 that includes the elastomer, the first freeradical initiator, the second free radical initiator, the third freeradical initiator, an unsaturated monomer, e.g., unsaturated carboxylicacid or the metal salt of the unsaturated carboxylic acid which may actas a crosslinking agent or other crosslinking agents, and optionallyfillers or other additives that may be homogeneously or heterogeneouslymixed throughout the piece 160. The piece 160 may, for example, becompounded in an extruder and extruded in a sheet or other appropriateform for further processing. In one embodiment, the compounded elastomeris partially crosslinked at the third crosslinking temperature in theextruder. In another embodiment, the elastomer is partially crosslinkedat the first and second crosslinking temperatures sequentially in theextruder so that piece 160 comprises the precursor compound. Theelastomer remains thermoplastic in the precursor compound.

The piece 160 may be formed into a substantially hemispherical blank 162(shown in FIG. 6B) through one or more cutting, stamping, or pressingprocesses. As schematically shown in FIG. 6C, two compression moldingdies 164, 166 may form a pair of opposing blanks 168, 170 about aspherical metal core 172. In another embodiment, a hemispherical shellis molded, for example by compression molding or injection molding,using a set of male and female molds. In an embodiment in which nocrosslinking of the elastomer polymer was carried out in the extruder,the forming of pieces 160 into a pair of opposing blanks 168, 170between the compression molding dies may include partial crosslinking atthe third crosslinking temperature to provide opposing blanks 168, 170of partially crosslinked elastomer or may include partial crosslinkingat both the third crosslinking temperature and the first crosslinkingtemperature to provide opposing blanks 168, 170 of the precursorcompound. In a further example, when the compounded elastomer ispartially crosslinked at the third crosslinking temperature in theextruder, the elastomer may be further crosslinked at the firstcrosslinking temperature in this step to provide opposing blanks 168,170 of the precursor compound.

Finally, as shown in FIG. 6D, the spherical metal core 172 may bereplaced by the center 16, and the blanks 168, 170 may be compressionmolded a second time by a second pair of opposing molding dies 172, 174(which may or may not be the same dies 164, 166 used in the prior step).During this stage, the dies 172, 174 apply a sufficient amount of heatand pressure to cause the blanks 168, 170 to flow within the moldcavity, fuse to each other, and crosslink to form the cured elastomerarticle. When the elastomer has experienced no crosslinking, the curemay be a two-stage cure, with partial crosslinking optionally at thethird crosslinking temperature, then partial crosslinking at the firstcrosslinking temperature to form the precursor compounds followed byfurther crosslinking of the precursor compound at the secondcrosslinking temperature to form the cured elastomer article. When theelastomer been partially crosslinked at the third crosslinkingtemperature, whether in the extruder or during forming of the opposingblanks 168, 170, the cure in the compression mold may be a two-stagecure, with partial crosslinking at the first crosslinking temperature toform the precursor compounds followed by further crosslinking of theprecursor compound at the second crosslinking temperature to form thecured elastomer article. When the opposing blanks 168, 170 have alreadybeen crosslinked to form the precursor compound, the opposing blanks168, 170 are further cured at the second crosslinking temperature in thecompression mold to form the cured elastomer article.

Once set, the intermediate ball (i.e., the joined center 16 andintermediate layer 18) may be removed from the mold.

The cover layer 24 may generally surround the core (in FIG. 4, enclosingouter intermediate layer 19), and the cover layer 24 defines theoutermost surface of the ball 112. The cover may generally be formedfrom a thermoplastic material, such as a thermoplastic polyurethane thatmay have a flexural modulus of up to about 1000 psi. In otherembodiments, the cover may be formed from an ionomer, such ascommercially available from the E. I. du Pont de Nemours and Companyunder the tradename Surlyn®.

The resulting golf ball formed from the elastomer compound includes acore and a cover disposed on and surrounding the core. In variousembodiments, the golf ball may be a two-piece ball having the core andthe cover or may be a multi-piece ball in which the core is made of acenter and an intermediate layer disposed between the center and thecover. FIG. 4 illustrates a four-piece ball with a core made up of acenter 16 and two intermediate layers 18 and 19 between the center 16and a cover 24. The center or one or both of the intermediate layers18,19 may be formed from the cured elastomer, which may increase acoefficient of restitution (COR) of the golf ball 112.

A coefficient of restitution (COR) for a golf ball may be measured byfiring the golf ball from an air cannon at an initial velocity of 40m/sec towards a steel plate positioned at about 1.2 meters apart fromthe air cannon. In addition, a speed monitoring device may be spacedapart from the air cannon over a distance of about 0.7 meters. After thegolf ball strikes the steel plate, the golf ball rebounds through thespeed-monitoring device at a return velocity. The coefficient ofrestitution for the golf ball is calculated by dividing the returnvelocity of the golf ball by the initial velocity of the golf ball.

The core comprises the cured elastomer, and the cured elastomer isformed from an elastomer compound comprising the ethylenicallyunsaturated elastomer, the first free radical initiator having the firstone-minute half-life temperature, and the second free radical initiatorhaving the second one-minute half-life temperature that is higher thanthe first one-minute half-life temperature by at least about 30° C. Theelastomer compound is partially crosslinked at the first crosslinkingtemperature that is equal to from about 20° C. lower than the firstone-minute half-life temperature to about 20° C. higher than the firstone-minute half-life temperature to form the precursor compound. Theprecursor compound is further crosslinked at the second crosslinkingtemperature that is higher than the first crosslinking temperature. Thesecond crosslinking temperature is equal to from about 20° C. lower thanthe second one-minute half-life temperature to about 20° C. higher thanthe second one-minute half-life temperature to thereby form the curedelastomer.

The golf ball 112 (FIG. 4) formed from the elastomer compound may havean excellent coefficient of restitution. As used herein, the terminology“coefficient of restitution” is a measurement of a resilience of thegolf ball 112. The coefficient of restitution may be calculated bydividing a return velocity of the golf ball 112 by an initial velocityof the golf ball 112 after the golf ball 112 strikes and rebounds from asteel plate.

The method 110 (FIG. 1) of forming the elastomer compound and the method110 (FIG. 3) of forming the golf ball 112 (FIG. 4) may contribute to theexcellent coefficient of restitution of the golf ball 112. Inparticular, partially crosslinking 20 (FIG. 1) the elastomer compoundwith the first free radical initiator at the first crosslinkingtemperature and further crosslinking 22 (FIG. 1) the precursor compoundwith the second free radical initiator at the second crosslinkingtemperature may provide the elastomer compound with excellent resilienceand softness as compared to other elastomer compounds which are notformed via the aforementioned dual-stage cure and dual-cure temperaturemethods 10,110.

The cured elastomer, and articles 12 (FIG. 2) formed from the curedelastomer, may have excellent physical properties. For example, thecured elastomer and articles 12 may have excellent resilience. Inparticular, partially crosslinking the elastomer compound with the firstfree radical initiator at the first crosslinking temperature and furthercrosslinking the precursor compound with the second free radicalinitiator at the second crosslinking temperature may provide the curedelastomer with excellent resilience and softness as compared to othercured elastomers which are not formed via the dual-stage cure anddual-cure temperature methods 10, 110. For example, the golf ball 112(FIG. 4) formed by the method 110 (FIG. 3) may have excellentelasticity, and may exhibit excellent durability over an operating lifeand acceptable spin during flight.

The following examples are meant to illustrate the disclosure and arenot to be viewed in any way as limiting to the scope of the disclosure.

EXAMPLES 1-8

To prepare each of the cured elastomers of Examples 1-8, components A-Gare combined in the amounts listed in Table 1 to form respectiveelastomer compounds.

The unit of measurement for the values listed in Table 1 for component Ais parts by weight. Further, the unit of measurement for the valueslisted in Table 1 for components B-G is parts by weight based on 100parts by weight of component A.

TABLE 1 Elastomer compound Components Example A B C D E F G Ex. 1 100 204 0.025 — 0.25 — Ex. 2 100 20 4 0.050 — 0.25 — Ex. 3 100 20 4 — 0.0200.25 — Ex. 4 100 20 4 — 0.035 0.25 — Ex. 5 100 20 4 0.025 — — 0.25 Ex. 6100 20 4 0.050 — — 0.25 Ex. 7 100 20 4 — 0.020 — 0.25 Ex. 8 100 20 4 —0.035 — 0.25

Component A is a high 1,4-cis polybutadiene rubber commerciallyavailable from Kumho Asiana Group of Seoul, South Korea.

Component B is zinc diacrylate, which is commercially available fromNippon Shokubai of Tokyo, Japan

Component C is zinc oxide, which is commercially available from AkzoNobel Polymer Chemicals LLC of Chicago, Ill.

Component D is dibenzoyl peroxide, which has a one-minute half-lifetemperature of about 131° C. and is commercially available from SigmaAldrich of St. Louis, Mo.

Component E is (1,1′ bis-t-butylperoxy)-3,3,5-trimethylcyclohexane,which has a first one-minute half-life temperature of about 152° C. andis commercially available from Akzo Nobel Polymer Chemicals LLC ofChicago, Ill.

Component F is di-t-butyl peroxide, which has a one-minute half-lifetemperature of about 193° C. and is commercially available from AkzoNobel Polymer Chemicals LLC of Chicago, Ill.

Component G is cumyl hydroperoxide, which has a one-minute half-lifetemperature of about 260° C. and is commercially available from SigmaAldrich of St. Louis, Mo.

Each of the elastomer compounds of Examples 1-8 is prepared by mixingthe components listed in Table 1 in an extruder. After thorough mixingin a first zone of the extruder, each elastomer compound is partiallycrosslinked in a downstream zone of the extruder at a first crosslinkingtemperature of about 150° C. for about five minutes to form therespective precursor compounds of Examples 1-8. The precursor compoundsare extruded and pelletized. Subsequently, each of the extrudedprecursor compounds of Examples 1-8 is further crosslinked duringcompression molding of the precursor compounds. In particular, eachprecursor compound is further crosslinked at a second crosslinkingtemperature of about 230° C. for about 15 minutes to form articles ofthe respective cured elastomers of Examples 1-8.

EXAMPLES 9-16

The same components A-G are combined in the amounts shown in Table 2using a two-roll mill to form elastomer compounds Examples 9-16 arecombined in the amounts listed in Table 1 to form respective elastomercompounds. The unit of measurement for the values listed in Table 2 forcomponent A is parts by weight, and the unit of measurement for thevalues listed in Table 2 for components B-G is parts by weight based on100 parts by weight of component A.

TABLE 2 Elastomer compound Components Example A B C D E F G Ex. 9 100 204 0.025 — 0.25 — Ex. 10 100 20 4 0.050 — 0.25 — Ex. 11 100 20 4 — 0.0200.25 — Ex. 12 100 20 4 — 0.035 0.25 — Ex. 13 100 20 4 0.025 — — 0.25 Ex.14 100 20 4 0.050 — — 0.25 Ex. 15 100 20 4 — 0.020 — 0.25 Ex. 16 100 204 — 0.035 — 0.25

Each of the elastomer compounds is introduced into a compression mold.For each elastomer compound of Examples 9-16, the compression mold isheated to 150° C., and the elastomer compound is crosslinked at thattemperature for five minutes to form a precursor compound. Then, themold is further heated to 230° C. and the precursor compound issubjected to a second crosslinking at that temperature for fifteenminutes to form a cured elastomer.

While the best modes for carrying out the disclosure have been describedin detail, those familiar with the art to which this disclosure relateswill recognize various alternative designs and embodiments forpracticing the disclosure within the scope of the appended claims. It isintended that all matter contained in the above description or shown inthe accompanying drawings shall be interpreted as illustrative only andnot as limiting.

What is claimed is:
 1. A method of forming a golf ball or a part of agolf ball, comprising: (a) providing a spherical component; (b)providing a mixture comprising an elastomer, a first free radicalinitiator, a second free radical initiator, and a member selected fromthe group consisting of unsaturated carboxylic acids, metal salts ofunsaturated carboxylic acids, and combinations thereof, wherein thefirst free radical initiator has a half-life of from about 0.2 minutesto about 5 minutes at a first crosslinking temperature, the second freeradical initiator has a half-life of from about 0.2 minutes to about 5minutes at a second crosslinking temperature, and the secondcrosslinking temperature is higher than the first crosslinkingtemperature by at least about 30° C.; and (c) in a mold, compressionmolding or injection molding the mixture around the spherical componentto cure the mixture and form a unitary layer of cured mixturesurrounding the spherical component, wherein the compression moldingstep (c) comprises heating the mixture in the mold at the firstcrosslinking temperature to partially crosslink the elastomer to a firstcrosslink density around the spherical component, then heating themixture in the mold at the second crosslinking temperature to furthercrosslink the elastomer to a final crosslink density around thespherical component.
 2. A method according to claim 1, wherein theelastomer comprises polybutadiene.
 3. A method according to claim 1,wherein the second crosslinking temperature is higher than the firstcrosslinking temperature by at least about 50° C.
 4. A method accordingto claim 1, wherein the first crosslinking temperature is from about100° C. and at most about 190° C., and wherein the second crosslinkingtemperature is from about 165° C. to about 280° C.
 5. A method accordingto claim 1, wherein the first free radical initiator is used in anamount of at most about 40 parts by weight based on 100 parts by weightof a total combined weights of the first free radical initiator and thesecond free radical initiator.
 6. A method according to claim 1, whereinthe heating at the first crosslinking temperature is carried out forfrom about 0.5 minute to about 15 minutes; wherein the heating at thesecond crosslinking temperature is carried out for from about 1 minuteto about 30 minutes.
 7. A golf ball formed by a method according toclaim 1, the golf ball having the spherical component, a cover, and atleast one intermediate layer between the spherical component and thecover, wherein the unitary layer formed is an intermediate layer.
 8. Agolf ball formed by a method according to claim 1, the golf ball havingthe spherical component, a cover, and at least one intermediate layerbetween the spherical component and the cover, wherein the unitary layerformed is the cover.
 9. A method of forming a golf ball or a part of agolf ball, comprising (a) forming a partially crosslinked mixture from aprecursor mixture by heating the precursor mixture in an extruder at afirst crosslinking temperature to crosslink the mixture to a firstcrosslink density at which the mixture is thermoplastic, wherein theprecursor mixture comprises an elastomer, a first free radicalinitiator, a second free radical initiator, and a member selected fromthe group consisting of unsaturated carboxylic acids, metal salts ofunsaturated carboxylic acids, and combinations thereof; (b) positioninga portion of the partially crosslinked mixture around a sphericalcomponent; (c) molding the spherical component and the partiallycrosslinked mixture in a mold to form a unitary layer of cured mixturesurrounding the spherical component wherein the molding comprisesmolding the spherical component and the partially crosslinked mixtureunder pressure while heating the partially crosslinked mixture at asecond crosslinking temperature that is higher than the firstcrosslinking temperature to further crosslink the partially crosslinkedmixture to form the cured mixture having a final crosslink density;wherein the first free radical initiator has a half-life of from about0.2 minutes to about 5 minutes at the first crosslinking temperature,the second free radical initiator has a half-life of from about 0.2minutes to about 5 minutes at the second crosslinking temperature andthe second crosslinking temperature is higher than the firstcrosslinking temperature by at least about 30° C.
 10. A golf ball formedby a method according to claim 9, the golf ball having the sphericalcomponent, a cover, and at least one intermediate layer between thespherical component and the cover, wherein the unitary layer formed isan intermediate layer.
 11. A method according to claim 9, wherein thesecond crosslinking temperature is higher than the first crosslinkingtemperature by at least about 50° C.
 12. A method according to claim 9,wherein the first crosslinking temperature is from about 100° C. and atmost about 190° C. and the second crosslinking temperature is from about165° C. to about 280° C.
 13. A method according to claim 9, wherein thefirst free radical initiator is used in an amount of at most about 40parts by weight based on 100 parts by weight of a total combined weightsof the first free radical initiator and the second free radicalinitiator.
 14. A method according to claim 9, wherein the heating at thefirst crosslinking temperature is carried out for from about 0.5 minuteto about 15 minutes; wherein the heating at the second crosslinkingtemperature is carried out for from about 1 minute to about 30 minutes.